CO2 and CH4 play a significant role in the global climate change and carbon circulation and can be used to monitor their origin and tectonic activity. In this paper, we carried out investigations on the gas compositions, carbon isotope ratios of CO2 and CH4, and He isotope compositions from the Qiangtang Basin and its adjacent areas. Our results show gas samples from Beiluhe, Bucha Lake, and eastern Tuotuo River are N2-rich with N2 over 75%. The contents of CO2 and CH4 are only 3.45%-20.91% and 0-3.58%, respectively. CO2/3He and CH4/3He and carbon isotopic values of CO2 and CH4 suggest that both CO2 and CH4 from Bucha Lake are biotic without mantle-derived CO2 and He, whereas those of Beiluhe and eastern Tuotuo River are abiotic. Southern Erdaogou Depot, branch of Tuotuo River, and Tanggula Mountain Depot are enriched in CO2 with more than 96%. The CO2 was at least partially originated from mantle, trace amount of CH4 was abiotic and derived from mantle-derived CO2; He was primarily originated from crust with only 2.15%-5.66% of mantle-derived origin. These results show that the emitting of large quantity of mantle-derived CO2 is likely to be ascribed to the presence of Bangong Lake-Nujiang River, Hoh Xil-Jinsha River sutures and the Cenozoic volcanism in northern Tibet. Nevertheless, the estimated small fraction of mantle-derived He may result from the low opening degree at the bottom of fault zones and possibly reflect a geological setting of strong extrusion and an increase in crustal thickness.
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There are many quartz vein-type tungsten polymetallic ore deposits in northern Guangdong which can be divided into two types according to their wall rocks. One type of the ore deposits is hosted in the Cambrian sandstones and coarse-grained granite while the tungsten polymetallic mineralization is closely related to the fine-grained granite, which is represented by the Miantuwo tungsten deposit. The age of fine-grain granite is dated to be 146.95±0.84 Ma/153.82±0.96 Ma, using zircon U-Pb method, while the molybdenite Re-Os isochrone and biotite Ar-Ar isochrone are 150.5±1.4 Ma and 151.0±1.2 Ma respectively, and thus the Miantuwo deposit was formed in the Late Jurassic. The other type of the ore deposits is hosted in the Devonian limestones with the Heshangtian tungsten deposit as a representative. The after type of ore deposits is different from the one aforementioned. 39Ar/40Ar dating of the micas from the Heshantian deposit shows that the mineralization age is 161.1±1.1 Ma, i.e., the deposit was also formed in the Late Jurassic. That is the quartz vein tungsten ore deposits in northern Guangdong are closely related to the Late Jurassic granites. Indosinian granites and the Devonian limestones can be the country rocks of the ore veins in northern Guangdong, and therefore, attentions should be paid to above two types of country rocks in the future explorations.
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